Dynamic Compression Sector (DCS) Project

Final Design and Testing of the DCS Pink Beam Stop

Jeff Collins, Jeremy Nudell, and Dana Capatina

Mechanical Engineering & Design Group Advanced Photon Source, AES Division

MEDSI 2014 Conference Melbourne, Australia – October 2014

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Outline:

• DCS Pink Beam Stop Requirements

• Brief Discussion of Pink Beam Stop Mechanical Design

• Pink Beam Stop Experimental Program • Conclusions

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DCS Pink Beam Stop Requirements:

Worst-Case DCS Beam Conditions

Requirements:

• The Pink Beam Stop must be able to stop the beam under the worst-case DCS beam condition

• The Pink Beam Stop must satisfy all personnel safety system (PSS) requirements

- The Pink Beam Stop must protect the downstream lead shielding under all conditions - The size of the beam strike area (229 mm W x 305 mm H) is defined by ray tracing

Desirable Operating Features:

• Detection of beam presence

• Ability of measure the total power of the beam

Conventional design criteria limits (Tmax < 300°C) are impractical because a grazing incidence angle < 0.5° would be required, and consequently, the beam stop length would be > 5 m.

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Dynamic Compression Sector (DCS) project

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DCS Pink Beam Stop Mechanical Design:

• All fittings are welded into the assembly and use Swagelok® VCR all-metal face seal gaskets • A cavity 12.95 mm deep is milled into the assembly behind the beam strike plate • A 6.35 mm thick copper plate is press fit into the bottom of the cavity leaving 6.6 mm deep

gas volume space behind the beam strike plate

Charge valve with locking device and cap

10 psig charge pressure

6.35 mm thick copper beam strike plate with

229 mm x 305 mm beam strike area

Pressure gauge for visual indication

50 psig burst disk

31.75 mm thick stainless steel body with 6.6 mm deep gas pocket cavity

Buna-N O-ring seal between strike plate and

assembly body

Pressure transmitter port

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Pink Beam Stop Pressure Set Points:

• The Pink Beam Stop is charged with air or nitrogen to a nominal system pressure of 10 psig

• The low pressure set point of 8.75 psig alerts the personnel safety system (PSS) system to close the front end photon shutter and stop the beam in the event that the beam-strike plate has been breached

• The high pressure set point of 11.5 psig alerts the beamline equipment protection system (BLEPS) system to close the beamline photon shutter and stop the beam so that the Pink Beam Stop will not exceed the safe touch temperature limit

Safe Touch Temperature Limit: 50°C

PCharge = 10 psig PLo = 8.75 psig PHi = 11.5 psig

Pink Beam Stop System Pressure as a Function of System Gas Temperature

System Pressure

(psig)

System Gas Temperature

(°C)

10.0 25.6

10.2 28.2

10.4 30.7

10.6 33.3

10.8 35.9

11.0 38.5

11.2 41.1

11.4 43.7

11.6 46.3

11.8 48.9

12.0 51.5

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Experimental Program Outline:

• Overview of laser system , test chamber and Pink Beam Stop prototype • Calibration of the weld head focal distance vs. delivered beam diameter

• Absorption of laser energy into bare copper • Maximum penetration depth in copper for the worst-case DCS beam condition • System pressure response with varying beam diameters and beam exposure locations • Pink Beam Stop minimum beam detection time • Using the Pink Beam Stop as a calorimeter

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Fiber Optic Laser System & Weld Head:

Laser System Specifications:

• Central Emission Wavelength: 1070 nm +/- 10 nm • Operational Modes: CW / Modulated • Rated Output Power: 400 W -0 W / + 10 W • Beam Diameter (1/e2): 5.0 mm +/- 0.7 mm • Full Angle Divergence: < 0.45 mrad • M2: < 1.10 • Emission Bandwidth: < 6.0 nm

FiberMini Weld Head with 100 mm Focusing Optic

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Calibration of the Laser Weld Head: Need to match the Total Power and Peak Heat Flux for the worst-case DCS beam condition using a fiber optic laser with a focusing weld head

Beam Diameter = 64 µm to match the worst-case beam condition

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Pink Beam Stop in the Laser System Test Chamber:

Thermocouple on right top corner of beam strike plate

Thermocouple on back center of the Pink Beam Stop assembly

Pressure tap to the Yokogawa differential pressure transmitter

Laser weld head & 90° beam bender

Yokogawa differential pressure transmitter & capillary line into the laser system chamber

• Pink Beam Stop is thermally isolated from the holder with 1/8” thick ceramic felt and ceramic washers on all mounting bolts

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Dynamic Compression Sector (DCS) Project

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Laser Power Absorption into Bare Copper:

• Absorption dramatically increases between 10,000 - 20,000 W/mm2 peak heat flux • Above ~ 25,000 W/mm2 peak heat flux the absorption is nearly 100%

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Pink Beam Stop Testing Conditions:

• All tests were conducted in air

• The laser beam was continuously applied onto the beam strike plate throughout each test

• The laser beam remained on until the system pressure reached just over 12.0 psig, requiring ~ 39 minutes of continuous exposure under worst-case DCS beam condition

• The system pressure and thermocouple data were recorded at a rate of 1 Hz using a customized LabVIEW program

• The surface damage caused on the beam strike plate was imaged using a 3-D optical

microscope system

• Samples were metallurgically sectioned in 15 µm increments across the damaged area to reveal the microstructure

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Maximum Penetration Depth:

• A leak developed after ~ 1 minutes with the 1.0 mm wall thickness case • The maximum penetration depth with the worst-case DCS condition was measured to be

1.1 mm ( Factor Of Safety > 5 with a 6.35 mm beam strike plate)

Metallurgical section of laser drilled hole in copper

100 µm

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System Pressure Response with Varying Beam Diameter Sizes and Beam Exposure Locations:

64 Micron Beam Diameter

5100 Micron Beam Diameter

5100 Micron Beam Diameter

Nanoparticle Carbon Absorption = 87.45% Applied 193.59 W to Absorb 169.3 W

• Pressure response insensitive to beam diameter

• Pressure response nearly independent of beam location

Nanoparticle carbon paint applied with an air brush

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Pink Beam Stop Minimum Beam Detection Time:

• The minimum beam detection time decreases with increasing applied power • For the worst-case DCS beam condition the beam can be detected in ~ 4 sec.

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System Pressure Response for Short Beam Exposure Times:

• System pressure response is rapid and very linear regardless of applied beam power • In each case here, only a few seconds are required to capture a linear pressure slope

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System Pressure Rise Slope at Various Beam Power Levels:

• The system pressure rise slopes from the previous plot are plotted against absorbed beam power and the results are very linear

• The Pink Beam Stop Can Be Used as an Accurate Calorimeter to measure beam power • The calorimeter measures Retained Power, not Absorbed Power • However, Absorbed Power ≈ Retained Power in the first few minutes of beam exposure because free

convection has not had sufficient time to influence the pressure rise slope

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DCS Pink Beam Stop Installation:

Four Pink Beam Stop assemblies have been installed in the DCS beamline

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Conclusions:

• The Pink Beam Stop will stop the beam under the worst-case DCS beam condition

• A breach in the beam strike plate can be positively identified by a drop in system pressure and this will trigger PSS to close the front end photon shutter

• Reaching the high pressure set point will trigger BLEPS to close the beamline photon shutter before the body temperature of the device exceeds a safe touch temperature of 50°C

• The Pink Beam Stop can detect the presence of the beam

• The Pink Beam Stop can be used as an accurate beam calorimeter

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The following slides were not presented at MEDSI2014 due to time limitations

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Dynamic Compression Sector (DCS) Project

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Laser System & Test Chamber:

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Dynamic Compression Sector (DCS) Project

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Verification of the Laser Power Output:

Laser Set Power (W)

Measured Power (W)

400 401.3

350 351.9

300 300.1

235 237.9

169.3 170.1

135 136.5

100 97.8

75 74.8

50 49.1

25 24.2

10 9.5

• Verified laser power output using a model #30 digital power probe by Optical Engineering Inc.

• Used two different heads to cover the power output

range from 400W to 10W • Meter error is +/- 3%

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Dynamic Compression Sector (DCS) Project

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Determination of the Beam Spot Size: • Tried burn tests on a variety of thin sheet materials to see which

would give the smallest hole diameter • For each material found the minimum applied power level

required to just burn through the material • Placed a copper block with a thermocouple mounted on the top

surface below the sample to be used as a beam switch • The beam is turned on and when the thermocouple temperature

rises 0.07°C (some of the photons begin penetrating through the material) this triggers the beam to shut off

• The beam on time is noted and the hole diameter is measured

using a 3-D optical microscope • Weld head focal distances set using precision shims • Performed 5 burn tests at 17 different weld head focal distances • We only take credit for the average hole diameter we can

measure at each weld head focal distance setting

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Dynamic Compression Sector (DCS) Project

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Pink Beam Stop Calorimetry: Minimum Detectable Power:

• We need to define a minimum system pressure rise slope where below this threshold the pressure rise slope signal is ignored

• Above this system pressure rise slope threshold we want positive identification of

beam presence and the ability to accurately measure the beam power

Worst Case:

• We consider a hutch air temperature rise of 10°F in a 1 hour period to be unlikely • If the hutch air temperature increases from 78°F to 88°F in 1 hour, then the pressure

rise slope will be ΔP/Δt = 0.0001276 psid/second • Using the System Constant = 70,520 Joules/psid found previously we can calculate

the minimum detectable beam power threshold

Minimum Detectable Beam Power = 9.0 Watts

We do not want nuisance beam presence alarms occurring from fluctuations in the hutch air temperature

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Dynamic Compression Sector (DCS) Project

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Why Using A Copper Plate & Thermocouple As A Beam Stop Will Not Satisfy PSS Requirements: Findings: 1. We have demonstrated under worst-case DCS off-normal beam conditions that the

maximum penetration depth caused by the beam strike will not exceed a depth of 1.1 mm

2. We have demonstrated that successive beam strikes on the exact same location will not drill the hole any deeper

Conclusions: 1. Although it is highly unlikely, successive beam strikes in the vicinity of an existing hole

can create a larger hole, and therefore it is possible to widen the hole and eventually drill through and breach the beam strike plate

2. The Pink Beam Stop will positively identify a breach in the beam strike plate and close the beamline photon shutter

3. A copper plate with a thermocouple used as a beam stop is unable to positively identify a breach in the beam strike plate Using A Copper Plate & Thermocouple As A Beam Stop Will Not Satisfy PSS Requirements